Cosmic rays sound like something out of a superhero comic: invisible, traveling close to the speed of light, they are constantly shooting toward (and through) Earth from outer space. But they are real—and with a little know-how, you can see them for yourself, no superpowers required.
Despite their name, cosmic rays are actually particles. Mostly protons and helium nuclei, they also include a grab bag of heavier atomic nuclei. When they collide with atoms in Earth’s atmosphere, they set off a shower of “secondary” particles that rain down on Earth.
You can’t see these subatomic particles directly, but using a cloud chamber, you can make their paths visible to the naked eye. In this video, NOVA’s
In this video, see stunning cloud chamber video of subatomic particles streaming off a radioactive rod.
Researchers now think that most cosmic rays come from supernova explosions, but the sources of very rare, ultra-high-energy cosmic rays, which carry energy that far exceeds anything produced at experimental particle accelerators like the LHC, are still a mystery.
Go Deeper
Editor’s picks for further reading
CERN:
Cosmic rays: particles from outer space
Get acquainted with the basics of cosmic rays in this primer from CERN.
Nature:
To catch a cosmic ray
The Pierre Auger Observatory in Argentina has observed dozens of ultra-high-energy cosmic rays, but their source remains a mystery. Nature News’ Katia Moskovitch asks what’s next for the observatory.
Pierre Auger Observatory:
The mystery of high-energy cosmic rays
What are high-energy cosmic rays, and where might they be coming from?
